1. Field of Invention
The present invention relates to a structure for multi-media. More particularly, the present invention relates to a structure for playing musical instrument digital interface (MIDI thereinafter) messages.
2. Description of Related Art
MIDI is the acronym of Musical Instrument Digital Interface, which is a protocol used for exchanging musical information among music synthesizers, musical instruments, and computers. Since the beginning of 80s, MIDI has been widely accepted and adopted by musicians and composers. MIDI is a standard language used by musical instruments and computers. It is a set of commands which instructs what musical instruments (i.e. MIDI equipments) should do and how to do it, for example, playing musical notes, raising volume, and producing sound effects, etc. MIDI is neither audio signal nor sound that is transmitted over MIDI cable, but a command sent to MIDI equipments or other apparatuses for playing a sound or executing certain action.
MIDI standard is popular mostly because of the following advantages:                1. The files generated are smaller, because MIDI files are commands rather than audio waveforms.        2. Editing is easier because editing commands is easier than editing audio waveforms.        3. It may be used as background music because MIDI music may be played along with other media such as digital video, graphics, animation, audio etc, to enhance the effect of the performance.        
FIG. 1 is a block diagram illustrating a conventional structure for playing MIDI messages. Referring to FIG. 1, in the conventional structure 100, the main-control element 101 loads all the tone colors from the wavetables 105 into the memory 107 in advance, then transmits the sequence data 103 to the MIDI synthesizer 109. According to the sequence data 103, the MIDI synthesizer 109 then reads the required tone colors from the memory 107 and synthesizes them into sound, and sends the synthesized sound to the output device 111. The sequence data 103 is MIDI messages. The wavetables 105 is stored in a low-cost and low access speed memory apparatus.
Since the tone colors of wavetables are directly loaded into the buffer memory for synthesis in the conventional structure, the capacity of the buffer memory is a very important for the conventional technology. A large capacity buffer memory is required if the MIDI messages played by a conventional structure with many tone colors. It is not only increases the manufacturing cost, but also limits the hardware extendibility of the conventional structure. The buffer memory needs to be replaced if the volume of tone colors required by the play MIDI messages is greater than the storage capacity of the buffer memory.